24点游戏（1 4 2 6）不可调换顺序，怎么组合

1: (4 - 1) (2 + 6)2: (4 - 1) (6 + 2)3: (4 (2 - 1)) 64: 4 (2 - 1) 65: 4 ((2 - 1) 6)6: (4 (2 - 1)) 67: 4 (2 - 1) 68: 4 ((2 - 1) 6)9: 4 (6 (2 - 1))10: 4 6 (2 - 1)11: (4 6) (2 - 1)12: 4 (6 (2 - 1))13: 4 6 (2 - 1)14: (4 6) (2 - 1)15: (2